A preliminary study on quality of knee strength measurements by means of Hand Held Dynamometer and Optoelectronic System

Strength measurements are popular in the clinical practice to evaluate the health status of patients and quantify the outcome of training programs. Currently a common method to measure strength is based on Hand Held Dynamometers (HHD) which is operator-dependent. Some studies were conducted on repeatability of strength measurements but they were limited to the statistical analysis of repeated measurements of force. In this work, the authors developed a methodology to study the quality of knee flexion/extension strength measurements by measuring the effective HHD position and orientation with respect to the patient. HHD positioning attitude was measured by means of an Optoelectronic System for which a marker protocol was defined ad-hoc. The approach allowed to assess quality of measurements and operator's ability by means of quantitative indices. The protocol permitted the evaluation of: angles of HHD application, angular range of motion of the knee and range of motion of the HHD. RMSE parameters allowed to quantify the inaccuracy associated to the selected indices. Results showed that the operator was not able to keep the subject's limb completely still. The force exerted by the subject was higher in knee extension and the knee range of motion was higher than expected, however the operator had more difficulties in holding the HHD in knee flexion trials. This work showed that HHD positioning should be as accurate as possible, as it plays an important role for the strength evaluation. Moreover, the operator should be properly trained and should be strong enough to counteract the force of the subject.